Benzothiazoles, synthesis

Scheme 41 Benzothiazole synthesis via copper-catalyzed cyclization-elimination...

Substituted benzothiazoles Synthesis and medicinal characteristics 13HC89. 

CS2 as a type of liquid sulfur source was applied in benzothiazole synthesis as well. In 2011, Ma and co-workers found that copper salt can catalyse the reaction between 2-haloanilines and dithiocarbamate, which was generated in situ from amines and carbon disulfide (Scheme 2.145a). ° 2-N-Substi-tuted benzothiazoles were produced in good yields. Later on, they found that thiols can be applied as well. Condensation of carbon disulfide with thiols in... 

Likewise, benzothiazole synthesis from thioamides 9 has been accomplished by a Cu(I)/Pd(11)-mediated ortho-C-H-functionaUzation/intramolecular C-S-bond formation process [365]. 

However, when 1,2-DAB 155a and benzaldehyde 252a were subjected to the oxidative cyclization conditions (Cho et al. 2012, 2013) used for benzoxazole and benzothiazole synthesis in the presence of a catalytic amount of NaCN, the expected benzimidazole 261 was not obtained (Scheme 2.35, Eq. 1). Instead, the corresponding imine was obtained as the major product along with an unexpected product in a slightly lower yield than the amount of NaCN used (Scheme 2.35, Eq. 2). When a stoichiometric amount of NaCN was used under the same conditions, the unexpected 3-phenyl 2-aminoquinoxaIine 262a was obtained as the major product (Scheme 2.35, Eq. 3) (Cho et al. 2014). 

From o-Aminothiophenols (Type A, S—C6H4—N -t- C).—o-Aminothiophenols continue to be widely used as starting materials in benzothiazole synthesis. Their interaction with monosaccharides or glucosides yields products of type (1) or (2). N-(Dichloromethylene)sulphonamides or N-aroyl-S-chloro-isothiocarbamoyl chloride furnish 2-acylamido-derivatives (3/ and (4). l,l-Bis(methylthio)-2,2-dicyanoethylene, dimethyl cyanimidodithioate, and 2,2,4,4-tetrarhethylcyclobutane-l,3-dione (i.e. the dimer of dimethylketen) produce benzothiazole derivatives of types (5), (6), and (7), respectively. 

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